The object of this invention is to provide an increased and more constant output volume telephone set for a universe of long distance talkers within a fixed range of sound pressures. The present telephone set and universe of local offices are deficient in volume output when sending to long distance trunk circuits through local plant cable losses. The extent of the deficiency was indicated by a limited Bell System volume survey in the 1950-1960 decade. The survey indicated a mean reduction from previous information to which the transmission systems was designed by about 12 vu. The output of the standard telephone is limited by local loop gain or "howl" margin in the two-wire telephones and loop around gain in four-wire transmission systems. A carbon granular transducer receives excitation current from the nearest switching office or it is supplied locally. When the current is supplied from the switching office, it is used to establish a request for service by a switchhook signal. The direct current path thus established is systematically interrupted to transmit the desired calling number to establish a connection at the switching office. The requirement for switchhook and calling number circuit limit the resistance permitted and provided in the local loop circuit to the switching office. The current delivered to the more distant transmitting transducer is but a fraction of that supplied on short calling loop circuits. In order to provide increased output with the longer local loop circuits, a dynamic type transducer can be used to reduce the current delivered from the switching office. Increased transducer response can be obtained by using transistor ampifiers for voice, switchhook and touch tone dialing. The object of this invention is to obtain increased sensitivity in the transducer circuit of the telephone and obtain increased output at a more constant volume with adequate and necessary howl and four-wire loop around margins. The output of the present telephone set could be increased by reducing the sensitivity of the receiver or receiving circuit and increasing the gain of the transmitting transducer and/or removing the so-called "equalizer" which introduces about 5 db of loss for shorter loops. A material reduction in the receiving sensitivity could be made to permit adequate transmitting signals but decreased receiving gains.
This invention permits increased and more constant volume from a hand set made up of a sound pressure to electrical signal transducer and a receiver to convert electrical signals to sound pressure waves. The talker signal either acoustic or electric is generally accepted as consisting of a convolution of components representing vocal cord timing, glottal pulses and vocal tract impulse responses that is f(A)t .times. f(B)t. The convoluted signal is separated by demodulation of the cross product into its components and selecting either component by appropriate filters. The frequency content of the demodulated voice signals extended from near direct current to those frequencies normally considered essential to understand the talker were measured. The amplitude of the informational signal is contained in the term f(A)t. When separated the individual terms can be relatively increased or decreased in amplitude as desired.